1. Field of the Invention
The present invention relates to a developing device which forms a toner image on a predetermined image carrying body, and to an image forming apparatus including the same.
2. Description of the Related Art
An image forming apparatus, such as a copying machine, a printer, a facsimile device, or a composite of these, which employs an electrophotographic method includes a developing device that forms a toner image on an image carrying body (for example, a photosensitive drums or transfer belt) by supplying toner to the image carrying body.
The developing device includes, as basic constituent elements, a developer storing portion which stores developer composed of a non-magnetic toner and a magnetic carrier, a developing roller which receives developer from the developer storing portion and forms a toner image on the image carrying body by supplying the developer to the image carrying body, and a regulating blade, disposed so as to oppose the circumferential surface of the developing roller, and regulating the layer thickness of the developer on the circumferential surface of the developing roller.
In order to form a good toner image on the image carrying body, it is important to form a developer layer having a uniform thickness on the circumferential surface of the developing roller, by means of a regulating blade. A first prior art technology is known as technology for achieving a uniform thickness of the developer layer.
The developing apparatus according to the first prior art technology includes a regulating blade constituted by a magnetic plate which is disposed opposite the circumferential surface of the developing roller, and a non-magnetic elastic plate which is attached to the downstream surface of the magnetic blade as viewed in terms of the direction of rotation of the developing roller. When the developer adhering to the circumferential surface of the developing roller passes a gap formed between the regulating blade and the circumferential surface of the developing roller, firstly, the thickness of the layer of the developer is regulated magnetically by the magnetic plate and then the layer thickness is regulated physically by the elastic plate. In this way, it is possible to achieve uniform thickness of the developer layer using the magnetic plate and the elastic plate.
However, in the developing device according to the first prior art technology, the gap between one end of the magnetic plate and the circumferential surface of the developing roller is liable to vary with the dimensional accuracy of the magnetic plate, and the installation accuracy of the magnetic plate in the developing vessel. Therefore, although one end of the elastic plate projects further toward the developing roller than one end of the magnetic plate, if the dimensional accuracy of the magnetic plate or the installation accuracy of the magnetic plate in the developing vessel, or the like, is poor, then there will consequently be variation in the gap between one end of the magnetic plate and the circumferential surface of the developing roller. In this way, in the developing device according to the first prior art technology, variation is liable to occur in the gap through which the developer layer passes, and therefore the layer thickness cannot be made uniform. As a result of this, it is difficult to form a good toner image on the image carrying body.